Heat exchanger with welded exchange plates

ABSTRACT

The heat exchanger comprises metal plates ( 6, 7 ) which have been press-formed and assembled in pairs by welding two opposite sides to make modular elements ( 2 ) that are stacked and which define two independent circuits for a first and a second fluid. The two metal plates ( 6, 7 ) of the modular element ( 2 ) are set flatly against each other over a predefined width (L) and are joined by solder ( 12 ) along this width and meant to ensure the mechanical cohesion of the assembly and by another solder ( 13 ) performed along the external edges of the plates and ensuring their sealing. The ends of the plates ( 6, 7 ) are welded to opposite connection partitions forming an exchange block which is itself mounted on four corner posts of the heat exchanger body.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to a heat exchanger with weldedheat-exchange plates, in order to achieve an exchange of heat between afirst fluid and a second fluid.

BRIEF DESCRIPTION OF RELATED ART

Already known, notably through European patent No. EP 0639258 B1 fromthe same inventor, is a heat exchanger with welded heat-exchange plates,of compact structure, bearing the commercial name “HEATEX” (registeredtrademark), comprising previously swaged metal plates, assembled by twosby welding on two opposite sides, and thereby forming stacked modularelements defining two independent circuits respectively for a firstfluid and for a second fluid. All the plates, thus joined, form aheat-exchange block of rectangular horizontal section, hence generallyparallelepipedal, which is assembled to four posts or corner uprightsbelonging to the frame of the heat exchanger. The open ends of thestacked modular elements are welded by being placed alongside oneanother on the edge of openings made in the opposite vertical connectingwalls of the heat-exchange block. The heat exchanger is closed by fourside doors screwed onto the uprights of the frame and easily removablefor maintenance.

In particular, European patent No. EP 0639258 B1 offers a solution whichremoves the stresses of differential expansion, between theheat-exchange block constituted by all the stacked plates, on the onehand, and the frame on the other hand, thanks to “corner gutters” thatare secured to the aforementioned connecting walls, and that partiallysurround the uprights of the frame, with the possibility of relativesliding.

Thanks to these arrangements, the heat exchanger according to Europeanpatent No. EP 0639258 B1 has advantageous features, in terms of behaviorat temperature, relative to the prior embodiments, also known, of heatexchangers with welded plates, such as those described in Europeanpatent applications EP 0165179 A and EP 0186592 A.

However, the heat exchanger with welded heat-exchange plates accordingto European patent No. EP 0639258 B1 still poses certain problems, andtherefore remains perfectable, for uses under considerablethermomechanical stresses.

In particular, when the heat-exchange block is set at temperature,because of the temperature gradient that prevails in service, theheat-exchange plates tend to expand lengthwise, in a directionperpendicular to the connecting walls situated at their ends. Thecorresponding expansion stress is calculated by the ratio F/S, F beingthe expansion force and S the section of the weld withstanding thisstress.

When the expansion is considerable, the stress is also and this mayresult in a breakage of the welds connecting the two plates associatedin a modular element, a breakage which occurs notably level with thezone where the heat-exchange plates and the adjacent connecting wall arealongside.

It is therefore appropriate to reduce the level of stresses at thislocation, in order to bring it to a value below the breaking threshold,by a reduction of the expansion force and/or by an increase of the weldsection.

BRIEF SUMMARY OF THE INVENTION

The invention provides enhancements to the heat exchanger with weldedplates, as described in European patent No. EP 0639258 B1, for thepurpose of enhancing its behavior at temperature, and notably to preventthe risk of breakage under the effect of the expansion stresses.

Accordingly, the essential subject of the invention is a heat exchangerwith welded heat-exchange plates, of the type considered above, that isto say comprising previously swaged metal plates assembled in twos bywelding on two opposite sides in order to form stacked modular elementsdefining two independent circuits respectively for a first fluid and fora second fluid, the ends of the heat-exchange plates being welded bybeing placed alongside one another on the edge of openings made in theopposite connecting walls, perpendicular to said plates, in order toform an overall parallelepipedal heat-exchange block which is assembledto four posts or corner uprights belonging to the frame of the heatexchanger, this exchanger being characterized in that, on their sides tobe assembled, the two swaged metal plates constituting each modularelement are on each side pressed flat against one another over apredefined width, are joined together by a first weld made in this widthand providing the mechanical cohesion of the assembly, and are alsojoined together along their outer edges by a second weld providing theseal.

Therefore, the invention replaces the usual “edge-to-edge” assembly ofthe two swaged plates with a particular configuration consisting incarrying out a “dimpling” of one of the plates and even of both plates,so that both plates are juxtaposed over a predefined width, preferablyat least equal to fifteen millimeters, allowing the achievement of adouble weld.

The first weld, which is a spot weld or a laser weld or an electrodewheel weld, ensures the mechanical cohesion of the assembly, that is tosay its resistance to pressure. The second weld, which is advantageouslya weld of the “TIG” or “plasma” type, for its part simply ensures theseal. The total weld section is therefore greatly increased, making theassembly of the plates much stronger.

According to another aspect of the present invention, each post orcorner upright of the frame of the heat exchanger with weldedheat-exchange plates has a beveled inner edge, the adjacent connectingwall being connected to the post or corner upright in the region of thisbeveled edge.

Therefore, when the heat-exchange plates tend to expand, they may takewith them the connecting walls which then comprise a possibility ofadditional deformation, by bending in the space released by the bevelededges of the posts or corner uprights. The expansion stress is thereforeabsorbed largely by the bending, now made possible, of the connectingwall.

According to an advantageous additional arrangement, each connectingwall comprises, in its two lateral zones, bellows-like conformations forits connection to the post or corner upright, in the region of thebeveled edge. The bellows-like conformations, which may each consistsimply of two inverted folds together forming a sort of sinewave,facilitate, as required, an expansion along an axis perpendicular to thedirection of longitudinal expansion of the heat-exchange plates. As iseasy to understand, the beveled edges of the posts or uprights offer afree space used here not only for the bending of the connecting walls,but also for the housing and the deformation of the bellows-likeconformations.

BRIEF DESCRIPTION OF THE DRAWINGS

In any case, the invention will be better understood with the aid of thefollowing description, with reference to the appended schematic drawingsrepresenting, as an example, one embodiment of this heat exchanger withwelded heat-exchange plates.

FIG. 1 is a partial and very schematic view, in exploded perspective,showing the general principle of assembling a heat exchanger of the typecovered by the present invention;

FIG. 2 is a view in cross section illustrating the current method ofassembling the plates of such an exchanger, on one of their sides;

FIG. 3 is a view in section similar to FIG. 2, but illustrating themethod of assembly according to the present invention;

FIG. 4 is a view in section passing through one of the corner zones ofsuch an exchanger, and illustrating the current method of connectionbetween a connecting wall and a post or corner upright;

FIG. 5 is a view in section similar to FIG. 4, but illustrating themethod of connection according to the present invention;

FIG. 6 is a view in horizontal section of a heat exchanger according tothe present invention;

FIG. 7 is a view in perspective showing a detail of the bottom portionof the heat exchanger of FIG. 6.

DETAILED DESCRIPTION OF THE INVENTION

With reference to FIG. 1, a heat exchanger with welded heat-exchangeplates comprises a series of modular elements 2, of generally square orrectangular shape, that are stacked and all assembled between twoopposite connecting walls 3, of rectangular shape, perpendicular to themodular elements 2.

These modular elements 2 have a very elongated section, and their endsare welded, by being placed alongside, on the edges of parallel openings4 arranged in the connecting walls 3.

These connecting walls 3 are themselves assembled, along theirlongitudinal edges (vertical in this instance), to posts or corneruprights 5, that are four in number. The bottom and top ends of theposts or corner uprights 5 are assembled, respectively, to a bottomsupport and a top support, not shown in FIG. 1, to form a completeframe, of generally parallelepipedal shape.

Inside this frame, which is closed on its lateral faces by doors notshown, all of the modular elements 2 form a heat-exchange block, itselfof generally parallelepipedal shape, which defines two independent fluidcircuits, namely a first fluid circuit consisting of the modularelements 2, and a second fluid circuit resulting from the free spacessituated between these modular elements 2. Inlet and outlet hoses, forthe two fluid circuits thus formed, are also provided.

For a more detailed description of this type of heat exchanger,reference is made to the aforementioned European patent No. EP 0 639 258B1.

With reference to FIGS. 2 and 3, each modular element 2 results from theassembly, on two opposite sides, of two metal plates 6 and 7 with atleast one of them being previously swaged.

More particularly, FIG. 2 illustrates the current method of assemblingthe two plates 6 and 7, on one of the sides (the other side being madein a symmetrical manner). The two plates 6 and 7 are in this instanceeach folded at 45°, one in the direction of the other, and a singlelongitudinal weld 8, of the “TIG” type, joins these two plates 6 and 7along their edges, brought one against the other.

Still considering one side of the modular element 2, the welded assemblyof the end of the latter to the connecting wall is carried out, in theillustrated example (for plates of a thickness of 1.5 mm), over asection of 2×2.8 mm×1.5 mm, or 8.4 mm², and this welded assembly has aconcentration of stresses at a point, level with the longitudinal weld8.

FIG. 3 illustrates the solution proposed here by the present invention.One of the plates 6 in this instance remains flat in the region of theside of the modular element 2, while the other plate 7 is made with a“dimpling”, that is to say that it has a first fold 9, for example at45°, followed by a second fold 10 for example at 45° but in thedirection opposite to the previous one, leading to the formation of alateral band 11 of width L, parallel to the main plane of the plate 7 inquestion.

By this lateral band 11, of width L, the plate 7 is pressed flat againstthe lateral region of the plate 6. The two plates 6 and 7 are thenjoined to one another, in the width L, by a first weld 12 which may be aspot weld or a laser weld or an electrode wheel weld, ensuring themechanical strength of the assembly.

The two plates 6 and 7 are also joined to one another, along their outeredges, by a second weld 13 which is notably a weld of the “TIG” type, bywhich in this instance simply the seal is ensured.

Advantageously, the two plates 6 and 7 are therefore juxtaposed in thelateral region of the modular element 2, over a width L equal to atleast fifteen millimeters.

Supposing that this width L is strictly equal to 15 mm, and everythingelse remaining equal, the embodiment according to the inventionachieves, at the assembly of the end of the modular element 2 to theconnecting wall, a weld section equal to: [(2×15)+5.6+4]×1.5 or 59.4mm², instead of the 8.4 mm² obtained with the current method ofassembly. The mechanically strong weld section is therefore multipliedby more than 7, in other words increased by more than 600%.

FIG. 4 represents, in horizontal section, one of the corner zones of aheat exchanger, showing a portion of a modular element 2 assembled to aconnecting wall 3, and a post or corner upright 5 belonging to the frameof the heat exchanger. More particularly, this FIG. 4 illustrates thecurrent method of connection between the connecting wall 3 and the postor corner upright 5, the latter having a usual square section. In thiscase, the connection has a rigidity at the two points P1 and P2, arigidity which opposes the free longitudinal expansion of theheat-exchange plates, in the direction of the arrow F.

FIG. 5 illustrates the solution proposed here by the present invention.The latter consists in beveling the inner edge of the post or cornerupright 5. More particularly, a 45° cut of the two adjacent faces 14 and15 of the post or upright 5 is made over a width of at least tenmillimeters, so as to form a bevel 16 which itself releases a free space17 of triangular section.

Therefore, when the modular element 2 tends to expand, in the directionof the arrow F, it may carry with it the adjacent connecting wall 3,which can bend by entering the free space 17, the first point ofrigidity P1 being removed. The expansion stress is therefore largelyabsorbed by the bending of the connecting wall 3.

In addition, as also shown in FIG. 5, the connecting wall 3 is connectedto the post or corner upright 5, in each lateral zone, by a bellows-likeconformation, resulting from two inverted folds 18 and 19, giving thiswall 3 locally (seen in horizontal section) a sinewave appearance. Thisbellows-like conformation introduces an additional zone of flexibility,making it easier, if necessary, for the heat-exchange block to expandalong an axis perpendicular to the direction of the arrow F.

FIG. 6, and FIG. 7 which represents a detail thereof, also illustrateadditional arrangements provided at the base and the top of the heatexchanger, to allow the expansion of the heat-exchange block on twoopposite sides. The bottom support of the frame in this instance beingmarked 20, each connecting wall 3 has, at its base, a portion 21deprived of openings 4 and folded to the horizontal above the bottomsupport 20, to which it is attached. On the portion 21 a longitudinalfold 22 is formed which makes it possible to absorb the expansion atthis location. Naturally, similar arrangements are provided in the topportion of the heat exchanger.

It should be noted that the heat exchanger described above may beproduced equally with swaged plates provided with a network of bosses,or dishes, or with swaged plates having parallel ribs or grooves, orelse with smooth plates provided with fitted mounting blocks, accordingto all configurations known per se. These heat-exchange plates mayconsist of simple metal sheets, for example made of stainless steel. Inparticular applications, they may also be metal sheets called “sandwich”metal sheets, made on one face with a stainless steel support layer,sufficiently thick to ensure resistance to the pressure, and on theother face by a thin layer made of precious metal or alloy, particularlynickel-based, tantalum-based or zirconium-based. It will be noted thatthe arrangements of the present invention are particularly suitable forassembling such “sandwich” metal sheets together. Specifically, with theusual technique, during the edge-to-edge welding of such metal sheets,there is a certain risk of a rise of ferrite in the melted metal core,by migration effect. The risk of corrosion is then considerable, theweld produced not having the characteristics of the precious metal. Onthe other hand, by, in this instance, applying the technique of thepresent invention, as illustrated by FIG. 3, with the use of metalsheets 6 and 7 of the “sandwich” type, the layer of precious metalprotrudes from the stainless steel support layer, and it is possible toproduce on the one hand the spot weld 12 ensuring the cohesion of theassembly, and on the other hand the sealing weld 13 of the “TIG” type,only by overlap between the two layers of precious metal or alloy whichprotrude from the respective stainless steel support layers.

Heat exchangers with welded heat-exchange plates, produced according tothe invention, may find industrial applications in varied fields: thechemical and pharmaceutical industry, the agribusiness industry, heatinginstallations, etc.

It goes without saying, and as emerges from the foregoing, that theinvention is not limited solely to the embodiment of a heat exchangerthat has been described above, as an example; on the contrary itembraces all the embodiment and application variants observing the sameprinciples. In this way, in particular, a user would not depart from thecontext of the invention:

-   -   by producing the heat-exchange plates in all shapes and        dimensions, in particular with generally square or rectangular        shapes and made of all weldable materials;    -   by producing the welds of these plates by using all appropriate        methods, whether they be the first weld or the second weld, for        example by producing the second weld with a “plasma” method;    -   by modifying the connection of the connecting walls with the        uprights or posts of the frame, the connecting walls not        necessarily being welded to the frame, but also being able to be        welded to intermediate parts, themselves applied about a post,        which notably travel over the beveled edge and the faces        adjacent the bevel and which may protrude over the next faces;    -   by using the heat exchanger not in a vertical position, but in a        horizontal position, according to the envisaged application, the        words “upright” and “post” in this instance having a purely        structural meaning but not implying a vertical orientation.

1. A heat exchanger with welded heat-exchange plates, comprising:previously swaged metal plates, assembled in twos by welding on twoopposite sides in order to form stacked modular elements defining twoindependent circuits respectively for a first fluid and for a secondfluid, ends of the heat-exchange plates being welded by being placedalongside one another on an edge of openings made in opposite connectingwalls, perpendicular to said plates, in order to form an overallparallelepipedal heat-exchange block which is assembled to four posts orcorner uprights belonging to a frame of the heat exchanger, wherein theswaged metal plates comprising each modular element are pressed flat oneagainst another over a predefined width, are joined together by a firstweld made in this width and providing mechanical cohesion of theassembly, and are also joined together along their outer edges by asecond weld providing the seal.
 2. The heat exchanger with weldedheat-exchange plates as claimed in claim 1, wherein the two plates arejuxtaposed over a predefined width at least equal to fifteenmillimeters.
 3. The heat exchanger with welded heat-exchange plates asclaimed in claim 1 or 2, characterized in that wherein the first weld(12) is a spot weld or a laser weld or an electrode wheel weld.
 4. Theheat exchanger with welded heat-exchange plates as claimed in claim 1,wherein the second weld is a weld of a “TIG” or “plasma” type.
 5. Theheat exchanger with welded heat-exchange plates as claimed in claim 1,wherein each post or corner upright of the frame has a beveled inneredge, the adjacent connecting wall being connected to the post or cornerupright in a region of this beveled edge.
 6. The heat exchanger withwelded heat-exchange plates as claimed in claim 5, wherein the bevel ofeach post or corner upright is made by a 45° cut of two adjacent faces,over a width of at least ten millimeters.
 7. The heat exchanger withwelded heat-exchange plates as claimed in claim 5, wherein eachconnecting wall comprises, in two lateral zones, bellows-likeconformations for connection to the post or corner upright, in theregion of the beveled edge.
 8. The heat exchanger with weldedheat-exchange plates as claimed in claim 7, wherein the bellows-likeconformations of the connecting walls each comprise two inverted foldstogether generally forming a sinewave.
 9. The heat exchanger with weldedheat-exchange plates as claimed in claim 1, wherein the heat-exchangeplates comprise “sandwich” metal sheets made on one face by a stainlesssteel support layer and on the other face by a thin precious metal oralloy, the sealing weld being made only by an overlap between the twolayers of precious metal or alloy which protrude from the respectivestainless steel support layers.